Heat-shrinkable article

ABSTRACT

Heat-resistant pressure-sensitive adhesives are used to form the closure of a heat-shrinkable wrap-around sleeve. Suitable pressure-sensitive adhesives include silicone-based adhesives, thermosetting acrylic adhesives, and thermosetting rubber/resin adhesives. However, silicone-based adhesives are not claimed herein, but are claimed in my co-pending application, Ser. No. 944,887, filed Sept. 22, 1978, now U.S. Patent No. 4,268,559, issued on May 19, 1981.

This is a continuation-in-part of my co-pending application, Ser. No.944,887, filed Sept. 22, 1978, now U.S. Pat. No. 4,268,559, issued onMay. 19, 1981.

BACKGROUND OF THE INVENTION

This invention relates to heat-shrinkable products which can be employedas seals on damaged pipes and conduits and as insulation on damagedelectrical conductors. More particularly, this invention relates toheat-shrinkable products which can function when no free end isavailable on the article to be protected. Such products are oftenreferred to as wrap-around sleeves. The major obstacle in producing sucha sleeve is the development of a closure device which can withstand theforces generated during shrinking at heat recovery temperatures.

U.S. Pat. No. 3,379,218 to Julian S. Conde discloses a heat shrinkablewrap-around sleeve whose closure consists essentially of button holesand buttons. This sleeve has the disadvantage of not being fabricated bythe inexpensive extrusion method, but by the more expensive moldingmethod. A further disadvantage of this sleeve is that, of necessity, thebutton holes and buttons are constructed of the same material as theheat-shrinkable portion. As such, when the sleeve is heated to softenthe heat-shrinkable portion for recovery to take place, the button holesand buttons may soften sufficiently so that the closure might fail.

U.S. Pat. No. 3,455,336 to Roger H. Ellis discloses a heat shrinkablewrap-around sleeve whose closure consists of elongated ridges along itsedges and a metal channel which slips over the ridges thus engaging theedges. The use of a metal channel has many disadvantages. In order toeffect a closure, the long metal fastener must be slid over the twoelongated ridges. This is a rather difficult operation, particularly ifthe closure is a long one. The weight of the wrap-around sleeve tends topull the two ridges apart before the metal fastener can be slid overthem. Further, the fastener can get stuck easily. Also, the resultingclosure is a raised strip along the sleeve covered with a metalfastener. If another cable is near the closure, the metal would rubagainst it causing damage. If the repaired cable has to be moved, theraised metal portion might catch on edges or other obstructions. If therepaired cable is rolled and unrolled as is the case with mine cables,the metal portion would rub against other parts of the cable, causingwear, would tend to catch and would be a safety hazard if it struck aminer. Furthermore, the metal in some instances might cause electricalproblems with the cable or other electrical equipment. Some of theproblems with the raised metal closure can be overcome by removing themetal fastener. However, after recovery of the sleeving, the fastener isso tightly held in place that it cannot be easily slid off. Thealternative is to cut off the protuberances with the metal fastener aswell. Not only is this an added time consuming step, but should therepairman cut into the sleeving itself, then the entire repair isuseless.

U.S. Pat. No. 3,530,898 to John R. Wilson discloses a heat shrinkablewrap-around sleeve whose closure consists of edges with a plurality ofloops and a metal rod which is passed through the loops. This sleeve hasthe disadvantage of requiring that the body of the sleeving must be cutand folded to produce the loops. A metal rod is required to hold theclosure together with the resulting problems as described in regards tothe Ellis Patent. But, perhaps the greatest disadvantage of this sleeveis the extreme difficulty encountered when inserting the rod into theloops, especially when the closure is a long one.

U.S. Pat. No. 3,574,313 to Ken Tanaka discloses a heat shrinkablewrap-around sleeve whose closure consists of slots on one edge andpreshrunk babs on the other edge. The preshrunk tabs on one edge areinserted into the corresponding slots on the other edge to form thesleeve. This sleeve has the disadvantage of the Conde closure in thatthe slots and tabs are constructed of the same material as theheat-shrinkable portion. As such, when the sleeve is heated to softenthe heat-shrinkable portion for recovery to take place, the slots andtabs may soften sufficiently so that the closure might fail. However,the greatest disadvantage of this sleeve is the extreme difficulty ininserting all the tabs into all the slots especially in a long closurewhere tabs may slip out of slots while other tabs are being insertedinto other slots.

U.S. Pat. No. 3,770,556 to Joseph H. Evans and Gareth W. Will disclosesa heat shrinkable wrap-around sleeve whose closure consists of edgeswhich overlap and have been coated with a contact adhesive. To preventthe overlapping edge from peeling back during recovery a restrainingmember consisting of a metallic foil coated with contact adhesive isadhered to the overlapping edge. This sleeve overcomes many of thedisadvantages of the previously-mentioned sleeve. It is simple for themanufacturer to fabricate. It does not require the use of metal faseningdevices. It does not relay on the same material as the heat-shrinkableportion of the sleeve for the closure device. However, it overcomesthese disadvantages by requiring the user of the sleeve to fabricate ineffect his own closure system. This sleeve requires that the user applycontact cement to the two edges of the heat-shrinkable member as well asto a sheet of material used to prevent the edges from peeling back.Should the manufacturer apply the contact cement, then the user isrequired to use solvents or heat to reactivate the adhesive.

Said U.S. Pat. No. 3,770,556 includes a review of the disadvantages ofcertain prior-art patents and patent applications, including thosehereinabove mentioned. Since said U.S. Pat. No. 3,770,556 is assigned tothe assignee of said prior art patents and patent applications, saidreview of their disadvantages is presumably authoritative. Said U.S.Pat. No. 3,770,556 states, at column 2 lines 13-15: "It had been thoughtthat no adhesive could withstand the force exerted by a heat recoverystep at the temperature of recovery," and asserts that the inventorsnamed in said patent discovered that some contact adhesives werepotentially capable of withstanding this force, and that such adhesivescan be used when peel-back tendencies are overcome.

Specific peel-back-prevention measures mentioned include the use ofcross-linking or the use of additional strips of metal or othermaterials or the use of a thin outer edge. Specific contact adhesivesinclude chloroprene based polymers such as neoprene. All the claims ofthis patent require separate peel-back prevention means.

In reviewing said prior art patents in the Amendment dated Oct. 10, 1972and filed Oct. 12, 1972, the applicants in said U.S. Pat. No. 3,770.556assert (at page 4 thereof): "As pointed out in the Specification of thisapplication, many solutions were found that would provide a suitablewraparound sleeve; however, they all required some mechanical connectionbetween the split edges of the sleeve to enable the sleeve to withstandthe substantial forces exerted by the heat recovery of the sleevingmaterial. It is the presence of the effects of recovery that would, andapparently did, dissuade those skilled in the art from attempting to usean adhesive to bond together the two edges of a split sleeve. Theeffects of recovery are manifested in two ways: first, a substantialshearing force is exerted in the area where the edges of the splitsleeve are brought together; second, the uppermost edge of the sleevetends to peel upwardly and away from the underlying edge. As a result ofthese effects, the workers in the prior art believed that a mechanicalconnection was necessary. We submit that it would not be at all obviousto one skilled in the art that an adhesive system could be provided thatwould withstand these two divergent effects of heat recovery, andwithstand them at temperatures approaching 200° C. where adhesive bondsare normally weakened but where a heat recoverable sleeve is typicallyheated to cause recovery. It was only the applicant's recognition that aspecific adhesive system, namely, a contact adhesive, when used inconjunction with means for preventing peel-back, could provide thesolution that previously eluded workers skilled in the art.

"Turning now to the claims, all elected claims 3, call for a heatrecoverable closure member having areas of a contact adhesive togetherwith means to prevent peeling back of the sleeve. When the closuremember is placed about a conductor or other longitudinal member, theareas of contact adhesive may be simply brought together to form asecure bond. None of the patents cited by the Examiner disclose acontact adhesive in any form and, instead, show pressure sensitive orother adhesives which would weaken with heating.

"Contact adhesives are not the same as pressure sensitive adhesives.Pressure sensitive adhesives, typified by the type of adhesives used onadhesive tape or cellophane tape have the characteristic of being stickyto the touch. In contrast, contact adhesives may exhibit little or nostickiness or tackiness until touched with another layer of contactadhesive. Such adhesives are typically applied to each of the twosurfaces to be joined and allowed to dry to a relatively tack freestate. These two surfaces are then brought together, at which time atight bond is formed. Thus, they exhibit autoadhesion or the ability tostick to themselves. In contrast, pressure sensitive adhesives willstick to most surfaces and feel sticky to the touch. Contact adhesivesare defined in applicants' Specification at page 13, lines 5 through 15and particular base polymers and formulations are described in theSpecification on pages 13 through 19.

"Turning now to the prior art of record, the patent to Carlson suggeststhe use of a "pressure sensitive adhesive tape" (see Carlson column 1,lines 62-64). Such a tape would not maintain strength at the elevatedtemperatures necessary to bring about heat shrinking. Thus, if a personfaced with applicants' problem of providing a wraparound closure sleevewere given the Carlson reference, he would find that the resultingsleeve would pull apart upon heating. It will now be shown that thesecondary references do not supply the deficiencies inherent in theCarlson reference when adapted to applicants' use . . . "

The foregoing excerpt from arguments made by the applicants of U.S. Pat.No. 3,770,556 show that, until the present applicant's inventiondisclosed and claimed herein, it was thought that pressure sensitiveadhesives were inoperative for use with heat-shrinkable materials.

SUMMARY OF THE INVENTION

If the closure of a wrap-around sleeve could be fabricated by usingpressure-sensitive adhesives rather than contact cement, then all thedisadvantages of the Evans and Will sleeve would be overcome as well asthe disadvantages of the sleeve of Conde, Ellis, Wilson and Tanaka. Sucha sleeve would be economical to fabricate and would be extremely easy touse. However, no pressure-sensitive adhesive was thought to havesufficient strength to withstand the forces exerted during heat recoveryat the temperature of recovery. The following types of heat resistantpressure-sensitive adhesives have been found which have sufficientstrength to withstand the forces exerted during heat recovery at thetemperature of recovery; thermosetting acrylic, thermosettingrubber/resin and silicone pressure-sensitive adhesives. I have alsofound that in order for these pressure-sensitive adhesives to produce aclosure sufficiently strong to withstand the shrink forces duringrecovery at the temperature of recovery, the adhesives must be attachedto a heat-stable portion of the wrap-around sleeve. I have found that aheat-shrinkable article comprising a heat-shrinkable sheet having twoedges adapted to form a closure made in accordance with the principlesof my invention will form a satisfactory closure if said edges are heatstable and if at least one of said edges has thereon apressure-sensitive adhesive adapted, after compression against the otherof said edges, to form a closure having a minimum lap-shear bondstrength of greater than approximately 1.0 psi at 300° F. to maintainsaid closure at a temperature sufficiently high to shrink saidheat-shrinkable sheet. The tenacity of the pressure-sensitive siliconeadhesive can be improved further by using a silane primer coat on theheat-stable edges.

One object of this invention is to provide a heat-shrinkable productwhich performs the function of a heat-shrinkable sleeve yet does notrequire the presence of a free end on the article to be protected.

Another object is to provide a heat shrinkable wrap-around sleeve whoseclosure does not require the use of a metal fastener as a closure means.

Another object is to provide a heat shrinkable wrap-around sleeve whoseclosure does not rquire the use of the same material as theheat-shrinkable portion of the sleeve.

Still another object is to provide a heat shrinkable wrap-around sleevewhose closure does not require the user to apply contact cements orsolvents or use heat to activate contact cements.

Still another object is to provide a heat shrinkable wrap-around sleevewhose closure consists of a heat-resistant pressure-sensitive adhesivewhich is easier to use than any other closure device hitherto provided.

Yet another object is to provide a heat shrinkable wrap-around sleevewhich is easy and inexpensive to manufacture.

Yet another object is to provide a heat shrinkable wrap-around sleevewhose closure consists of a heat-resistant pressure-sensitive adhesiveand a locating and holding device to ensure that the pressure-sensitiveadhesive is perfectly aligned before joining.

The term "pressure sensitive adhesive", used in applicant's claims, hasacquired a definite meaning in the art, and is quite distinct from theterm "contact adhesive", used in Evans, et al U.S. Pat. No. 3,770,556.

Thus for example, at page 548 of "Handbook of Adhesives", secondedition, by Irving Skeist (van Nostrand Reinhold Company 1977) it isstated: "Pressure-sensitive adhesives form a permanently tacky filmafter the evaporation of the liquid phase or after cooling of ahot-melt." Pressure-sensitive adhesives are distinguished from contactadhesives at page 28 of the same text.

Pressure-sensitive adhesives are also distinguished from contactadhesives at page 20 of "The Encyclopedia of Chemistry", Third Edition,by C. A. Hampel and G. G. Hawley (van Nostrand Reinhold Company 1973).

See also the Table of Contents of "Adhesives 1978/79" CorduraPublications, Inc.).

Evans, et al., of course, furnished their own definition of the term"contact adhesive" at column 5, lines 64 et seq. of their U.S. Pat. No.3,770,556. During prosecution of the corresponding patent application,Evans, et al. stressed the distinction between contact adhesives andpressure-sensitive adhesives, as pointed out hereinabove.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The foregoing and other objects of the invention will become apparentupon referring to the following detailed description and theaccompanying drawings, in which:

FIG. 1 is a transverse section of a tubular article formed from aheat-shrinkable sheet embodying the invention prior to closure;

FIG. 2 is a transverse section of the tubular article of FIG. 1 afterclosure and after recovery; and

FIG. 3 is a detail of a transverse section similar to that of FIG. 1showing a preferred embodiment of the invention.

Referring to the drawings, and first to FIG. 1 thereof, a sheet 1 ofappropriate material, such as polyethylene, is extruded, cross-linkedand expanded by conventional techniques. The extruder is so constructedas to give a profile to the sheet, so that the extruded sheet 1 hasedges 2, 3 which are half the thickness of the body 4 of the sheet. Theextruded sheet 1 is then expanded preferentially; that is, the body 4 isexpanded and made heat unstable while the edges 2, 3 remain unexpandedand are therefore heat stable. Such expansion lengthens the body 4 ofthe sheet 1 and in so doing, reduces its thickness, so that thethickness of the heat-unstable body 4 of the sheet 1 becomes about thesame as that of the heat-stable edges 2, 3. Pressure sensitive adhesivetapes 5, 6 with release papers 7, 8 are located on the heat-stable edges2, 3.

Referring now to FIG. 2, therein is shown the heat-unstable wrap-aroundsleeve of FIG. 1 after recovery. During recovery the length of the body4 of the sheet 1 shortens and, in so doing, increases its thickness, sothat the thickness of the heat-stable edges 2, 3 is now about one-halfthe thickness of the recovered body 4. Consequently, the recoveredsleeve has essentially uniform thickness, and a raised edge which mightcatch or lift during use is avoided.

FIG. 3 shows an embodiment of the invention in which the substrate is sodesigned that an aligning and holding device is built into it. To thatend, a raised ridge 9 is produced on the end of heat-stable edge 3'. Onan interior portion of heat-stable edge 2', behind pressure-sensitiveadhesive tape 5', there is produced a recessed channel 10. The raisedridge 9 and the recessed channel may be produced, for example, bysuitable design of the extruder die. Raised ridge 9 is pressed intorecessed channel 10 to align and hold the closure together. Once inposition, the release papers 7,', 8' on the surface ofpressure-sensitive adhesive tapes 5', 6' are removed, and the twoadhesive tapes 5', 6' now perfectly aligned are pressed together to forma closure ready for heat-shrinking.

Preferably the adhesive tape 5, 6 is a double-coated, pressure-sensitiveadhesive tape or else a pressure-sensitive transfer tape. Adouble-coated tape consists of a sheet of paper, plastic or the like,which has been coated on both sides with a pressure-sensitive adhesive.A release paper as shown at 7, 8 is used on one side so that the tapecan be rolled up and unrolled satisfactorily. When the tape is unrolledfor use, it sticks to the release paper, exposing one pressure-sensitivesurface. The tape can be applied to almost any surface with the releasepaper protecting the other pressure-sensitive surface. When the secondsurface is to be used, the release paper is removed and the secondpressure-sensitive surface can be applied to whatever surface isdesired. In this way, two surfaces can be easily attached to oneanother. A pressure-sensitive transfer tape consists of a sheet ofpressure-sensitive adhesive coated onto a release paper. It functionsthe same way as a double-coated, pressure sensitive adhesive tape. Manysuch double-coated or transfer pressure-sensitive tapes are commerciallyavailable. In the catalog "Scotch Industrial Tapes" published by theTape and Allied Products Group of 3M Company, St. Paul, Minnesota arelisted over 30 such tapes. Similar tapes are also sold by NashuaCorporation, Nashua, N.H., Permacel Corporation, New Brunswick, N.J.,The Kendall Company, Boston, Mass., Dennison Manufacturing Company,Framingham, Mass., Bostik Division, USM Corporation, Middleton, Mass.,and National Adhesives Division, National Starch and ChemicalCorporation, Bridgewater, N.J. Double-coated or transferpressure-sensitive adhesive tapes recommended for high temperature usewere obtained from these companies and tested for bond strength at 300°F.

Two substrates for testing the pressure-sensitive adhesive were selectedas typical heat shrinkable sleeve materials. One substrate consisted ofabout 65% polymer of ethylene and vinyl acetate, 30% flame retardantsand lesser amounts of antioxidants, radiation sensitizers and processingaid. The material was extruded into a 0.040 inch thick sheet andirradiated at 10 MR. The sheet was cut into 1 by 3 strips. The othersubstrate consisted of about 73% low-density polyethylene, 22% flameretardants and lesser amounts of antioxidants and stabilizer. Thematerial was extruded into a tube with a 11/2 inch outside diameter anda wall thickness of 0.050 inches. The tubing was irradiated at 15 MR,slit longitudinally and the resulting sheet was cut into 1 by 3-inchstrips. Specimens for testing the pressure-sensitive tapes were preparedby pressing two 1-inch squares of tape onto two 1 by 3-inch strips ofthe substrate. The tapes were attached so that they abutted a 1-inchedge of the strip.

Pairs were allowed to build adhesion overnight. The next day the releasepapers were removed from the pressure-sensitive tapes, and the stripswere pressed together, adhesive tape to adhesive tape. The result was a5-inch long test specimen with a 1-inch square overlapped bondedportion. Specimens were heated at 300° F. in an air circulating oven for5 minutes and then pulled apart at a rate of 1 inch per minute in anInstron tester equipped with an air circulating oven set at 300° F. Themaximum bond strength in pounds per square inch obtained is recorded inTable I.

                                      TABLE I                                     __________________________________________________________________________    BOND STRENGTH AT 300° F.                                                            POUNDS PER SQUARE INCH                                                  TAPE  ETHYLENE VINYL                                                                             POLYETHYLENE                                        COMPANY                                                                              NUMBER                                                                              ACETATE SUBSTRATE                                                                          SUBSTRATE ADHESIVE TYPE                             __________________________________________________________________________    PERMACEL                                                                             P-257 3.1          2.4       Thermosetting rubber/resin                PERMACEL                                                                             P-905 1.9          --        Silicone                                  BOSTIK 10-610-2                                                                            3.2          --        Thermosetting acrylic                     DENSIL 1078  2.6          2.0       Silicone                                  __________________________________________________________________________

PERMACEL P-257 is a rubber, resin, thermosetting pressure-sensitiveadhesive, coated both sides on a 1-mil electrical polyester film withred flat release paper. PERMACEL P-905 is a silicone pressure-sensitiveadhesive on a polyester film backing with a cloth release liner. Bostik10-610-2 is a pressure-sensitive acrylic adhesive. Densil 1078 is aphenyl containing silicone pressure sensitive adhesive.

In an effort to improve the bond strength of the Densil tape to thesubstrate, a number of silane adhesion promoters were evaluated. Thesesilanes produced by Union Carbide Corporation, Chemicals and PlasticsDivision, New York, N.Y. were dissolved at 1% concentration intoisopropyl alcohol and painted onto the substrate described above. Twosheets of substrate were used: one irradiated at 10 MR, the other at 30MR. In this way, both the effect of silane adhesion promoters andirradiation dosage on Densil bond strength were determined. The bondstrength test at 300° F. was run as described above. Results are listedin Table II. These results indicate that the use of silane adhesionpromoters, particularly A-1100 and A-1120 increase the hot bond strengthof Densil silicone tape to this substrate. Also, the hot bond strengthof Densil tape increases with increased irradiation of the substrate.

                  TABLE II                                                        ______________________________________                                        300° F. Bond Strength of Densil 1078 Tape                              Pounds Per Square Inch                                                                       10 MR.      30 MR.                                             PRIMER COAT    SUBSTRATE   SUBSTRATE                                          ______________________________________                                        Isopropyl Alcohol                                                                            1.8         4.2                                                Isopropyl Alcohol +                                                                          1.7         4.6*                                               1% A-172 Silane                                                               Isopropyl Alcohol +                                                                          2.0         3.9                                                1% A-174 Silane                                                               Isopropyl Alcohol +                                                                          2.9*        5.4*                                               1% A-1100 Silane                                                              Isopropyl Alcohol +                                                                          2.6*        4.6*                                               1% A-1120 Silane                                                              ______________________________________                                         *The substrate on these samples broke before the bond failed. The other       samples were all bond failures.                                          

The substrate for use in producing a heat-shrinkable wrap-around sleevecan be selected from any material which exhibits the property of elasticmemory. By elastic memory is meant the property of a material which canbe deformed upon heating, and when cooled in the deformed shape willretain the deformed shape, yet when reheated will return to its originalundeformed shape. Of particular interest are polymer formulationscontaining cross-linked crystalline polymers such as polyolefins, olefincopolymers and the like.

An economical, simple way of fabricating a wrap-around sleeve is toextrude a sheet of appropriate material, cross-link it and expand itusing a longitudinal stretcher such as the type manufactured by Marshalland Williams Company, Providence, R.I. The sheet can be cut intoconvenient sizes, and two surfaces along opposite edges recovered byheating. Then, by attaching pressure-sensitive, double-coated ortransfer tapes to the recovered, heat-stable upper surface of one edgeand the recovered, heat-stable lower surface of the opposite edge, asatisfactory wrap-around sleeve is produced. The user wraps this sleevearound the item to be repaired, attaches the tapes to each other andusing heat, shrinks the resulting sleeve to produce the repair. It ispossible to use a closure consisting of one tape instead of two; buttapes develop almost instantaneous adhesion to themselves while theiradhesion to non-porous plastics tends to build with time. Therefore, itis preferred to use two tapes. Also, if one tape is used, then theclosure would require that the tape adhere directly to the surface ofthe sleeve. If the sleeve got wet or dirty during application, thismight interfere with the obtaining of a satisfactory bond. If two tapesare used, each with a release paper to protect its surface, thepossibility of obtaining a satisfactory bond is improved.

Another economical, simple way of fabricating a wrap-around sleeve is toextrude a tube, cross-link it and expand it on a tube expander such asthe one disclosed in U.S. Pat. No. 3,086,242. The tube can then be slitlongitudinally to produce an expanded sheet. This sheet can then befabricated into a wrap-around sleeve using the procedure describedabove.

A problem with the above-described wrap-around sleeves is that theentire substrate is the same thickness. As a result, when the sleeve isshrunk down, the portion of the sleeve which is overlapped is at leasttwice the thickness of the rest of the sleeve. This leaves a raised edgewhich might catch and lift during use. This problem can be overcome bymolding or extruding a profile of the type shown in FIGS. 1 and 2 ratherthan a simple sheet, the profile having edges which are half thethickness of the rest of the sheet. As noted above, these edges arerendered heat stable, so that pressure-sensitive adhesive tapes can beattached to the heat-stable edges with no concern for the loss of bondstrength inherent in heat-unstable substrates.

Still another problem with wrap-around sleeves of the types describedabove is related to the fact that two pieces of pressure-sensitiveadhesive tape are used to form the heat-resistant closure. Althoughthere are many advantages to using two pieces of pressure-sensitiveadhesive tape to form the closure, there is one disadvantage. Becausethe pressure-sensitive adhesive has almost instantaneous adhesion toitself, if the two tapes are misaligned when brought into contact, theyare difficult to separate. This problem can be overcome by designing thesubstrate so that an aligning and holding device is built into it. Oneform of such a device is shown in FIG. 3 and consists of a raised ridgeon the end of one heat-stable edge and a recessed channel on theinterior part of the other heat-stable edge. The raised ridge is pressedinto the recessed channel before the pressure-sensitive tapes arepressed together. After the aligning and holding device has beenengaged, the release papers are peeled off and the pressure-sensitiveadhesive tapes, now prefectly aligned, are pressed together.

The following examples serve to illustrate the invention, but they arenot intended to limit it.

EXAMPLE 1

The following formulation was prepared in an FCM continuous mixer:

    ______________________________________                                                           PERCENT                                                    ______________________________________                                        Ethylene Vinyl Acetate Polymer                                                                     66.4                                                     Flame Retardants     29.9                                                     Antioxidant          2.0                                                      Radiation Sensitizer 1.3                                                      Processing Aid       0.4                                                                           100.0                                                    ______________________________________                                    

The formulation was extruded to produce a sheet 26-inches wide and0.040-inch thick. The film was stretched 100% on a longitudinalstretcher produced by the Marshall and Williams Company, Providence,R.I. The film was irradiated at 10 MR after which it had 60% expansion,the remaining stretch having been "locked-in" by the irradiation. A 10by 4-inch piece, 10 inches in the expanded direction was recovered 11/2inches along its 4-inch edges. The resulting piece was about 9 by 4inches and had 1-inch wide recovered sections along its 4-inch edges.One-inch wide Densil No. 1078 pressure-sensitive silicone transfer tapewith release paper was pressed onto the upper surface of one recoverededge and the lower surface of the other recovered edge to form awrap-around sleeve. The tape was allowed to build adhesion to thesubstrate overnight. The next day the release papers were removed fromthe two pieces of tape, and the tapes were firmly pressed together toform a tube. A pair of cylindrical mandrels 11/2 inch and 7/8 inch indiameter were placed into the tube. The tube was shrunk down firmly overthe mandrels using a propane torch. The closure held securely even whenheated vigorously with the torch.

EXAMPLE II

The following formulation was prepared in an FCM continuous mixer:

    ______________________________________                                                         PERCENT                                                      ______________________________________                                        Low Density Polyethylene                                                                         73.0                                                       Flame Retardants   21.5                                                       Antioxidant        3.7                                                        Stabilizer         1.8                                                                           100.0                                                      ______________________________________                                    

This formulation was extruded to produce a 11/2-inch diameter tube witha 0.050-inch thick wall. The tube was irradiated to produce a tube witha modulus at 300° F. of 30 psi. The tube was expanded to a 3-inchdiameter and a wall thickness of 0.025 inches. The tube was slit alongits center to produce an expanded sheet 9.4-inches wide. Pieces 5-incheslong were cut from this sheet. Strips 2-inches wide along the 5-inchedges of the pieces were recovered. The resulting pieces were 7.4 by 5inches and had 1-inch wide recovered strips along their 5-inch edges.One-inch wide Densil No. 1078 pressure-sensitive silicone transfer tapewith release paper was pressed onto the upper surface of one recoverededge, and the lower surface of the other recovered edge to form awrap-around sleeve. A similar sleeve was made using Permacel P-257pressure-sensitive, double-coated thermosetting tape. The tapes wereallowed to build adhesion to the substrate overnight. The next day therelease papers were removed from the two pieces of tape on each sleeve,and the tapes were firmly pressed together to form tubes. A pair ofcylindrical mandrels 11/2 inches and a 1/2 inch in diameter were placedin the tubes. The tubes were shrunk down firmly over the mandrels usinga propane torch. The closures held securely even when heated vigorouslywith the torch.

The following tests, which were conducted under conditions comparable tothose of Example II, were performed under my direction.

EXAMPLE II-A

This is not an example of the present invention.

The 3-inch diameter irradiated and expanded tube described in saidExample II was slit into a 9.4-inch sheet and cut into a 5-inch strip.Sears Non-flammable Chlorinated Contact Cement No. MY-80655 was appliedto a 2-inch wide strip on the upper surface of one 5-inch edge and to a2-inch wide strip on the lower surface of the other 5-inch edge. A2-inch wide, 5-inch long strip of aluminum foil was also coated withthis contact cement.

The solvent was allowed to evaporate from the contact cement for about10 minutes and the two contact cement-coated surfaces were pressedtogether forming a tube. The 2-inch wide strip of contact cement-coatedaluminum foil was pressed onto the joint of the tube so that 1-inch wideportions of the strip were on each side of the joint.

A cylindrical mandrel 11/2 inches in diameter was placed in the tube,and the tube was shrunk down firmly over the mandrel using a propanetorch. This is an example of a wrap-around repair sleeve as taught byU.S. Pat. No. 3,770,556.

EXAMPLE II-B

This is not an example of the present invention.

The 3-inch diameter irradiated and expanded tube described in saidExample II was slit into a 9.4 inch sheet and cut into a 5-inch strip.Sears Non-flammable Chlorinated Contact Cement No. MY-80655 was appliedto a 2-inch wide strip on the upper surface of one 5-inch edge and to a2-inch wide strip on the lower surface of the other 5-inch edge. Todemonstrate the difference between a contact cement and apressure-sensitive adhesive, this assembly was allowed to dry overnight.The next day the assembly was completely useless as a heat-shrinkablerepair sleeve. The two contact cement covered edges of theheat-recoverable sheet were pressed together, but they did not sticktogether. The contact cements no longer had any tackiness. As is wellknown in the art, contact cements lose their tack properties withinhours of their application. This means that to use contact cements as aclosure device for a repair sleeve, the individual who is repairing thesleeve must apply the contact cement within minutes before repairing thesleeve. This can often be difficult or impossible. For example, manyrepair sleeves are used to repair cables in underground mines, where thevolatile and possibly flammable solvents in a contact cement would notbe allowed because of safety regulations. Also in many cases, the repairsleeve is used in areas which are wet and dusty. Should the sleeveitself become wet or dusty, the application of a satisfactory film ofcontact cement would be difficult.

On the other hand, the closure method described and claimed hereinconsists of a pressure-sensitive adhesive. Unlike contact cements, whichlose their tackiness in hours, pressure-sensitive adhesives retain theirtack for many months. As a result, the repair sleeve described hereincould be fabricated by its manufacturer, sold to the user who could usethe sleeve months after its fabrication and still not be required toapply any adhesive. The pressure-sensitive adhesive applied duringmanufacture of the sleeve would still be tacky and functional.

Contact cements once dried out and non-tacky can be made tacky byapplying solvent to their surface or by applying moderate heat. Boththese methods of making a contact cement tacky are unsatisfactory forthe present product. The use of solvents presents the same problem asthe use of contact cements mentioned above. In underground mines whererepair sleeves are often used, solvents are not allowed because of theirvapors and flammability. The use of moderate heat to make non-tackycontact cement tacky once more also presents a problem. In mines or inoutdoor locations where repair sleeves are usually used, a source ofmoderate heat is not available. Heat-shrinkable repair sleeves areusually shrunk down by the use of a propane gas torch or other suchtorch. Such a torch would be available to the repair sleeve user.However, to moderately heat the contact cement, in order to regenerateits tackiness, using a propane torch without prematurely shrinking theheat-shrinkable sleeve upon which the contact cement is applied, wouldbe a rather difficult task. How much simpler it would be to use a repairsleeve whose heat-stable closure consisted of a pressure-sensitiveadhesive tape.

EXAMPLE III

The following formulation was prepared on a hot 2-roll mill:

    ______________________________________                                                           PERCENT                                                    ______________________________________                                        Ethylene Vinyl Acetate Polymer                                                                     66.4                                                     Antioxidants         2.0                                                      Radiation Sensitizer 1.3                                                      Flame Retardants     29.9                                                     Processing Aid       0.4                                                                           100.0                                                    ______________________________________                                    

A sheet of this material was inserted into a compression mold and heatedto 300° F. under 20 tons of pressure. After a 10-minute heating cycleand subsequent cooling, a flat plastic part with a profile as shown inFIG. 2 was removed from the mold.

The molded piece was irradiated at 10 MR. At 300° F. this piece had a100% modulus of 46 psi, a tensile strength of 76 psi, and an elongationat break of 257%. The 1-inch thin sections of the piece were clampedbetween metal strips using C-clamps. The center portion of the plasticpiece was immersed for 5 minutes in a heat-transfer medium heated to300° F. The metal strips and about a 1/2-inch long section of theplastic piece were not immersed in the heat-transfer medium. After theheating cycle, the section that had been heated was stretched to twiceits length and cooled in the stretched condition. The expanded piece hada profile as shown in FIG. 1.

One-inch wide pressure-sensitive silicone transfer tape with a releasepaper was attached to the molded piece on the top of one unexpandededge, and the bottom of the other unexpected edge. Also, a sheet ofhot-melt adhesive was attached to the molded piece by wiping it withsolvent and pressing it onto the inside surface of the sleeve.

The transfer tapes were allowed to build adhesion to the plastic pieceovernight. The next day the plastic piece was wrapped around a 2-inchdiameter cable. The hot-melt adhesive side of the piece was against thesurface of the cable. The release papers were removed and the siliconetransfer tapes were pressed together. The resulting sleeve was shrunkaround the cable using a propane torch. The sleeve formed a tight fitaround the cable with no slippage of the silicone transfer tapes duringthe heat-shrinking process.

EXAMPLE IV

The following formulation was prepared on a hot 2-roll mill:

    ______________________________________                                                           PERCENT                                                    ______________________________________                                        Ethylene Vinyl Acetate Polymer                                                                     57.8                                                     Antioxidants         1.7                                                      Radiation Sensitizer 1.1                                                      Flame Retardants     26.0                                                     Processing Aid       0.4                                                      Reinforcing Filler   13.0                                                                          100.0                                                    ______________________________________                                    

A sheet of this material was molded in a compression mold at 300° F.under 20 tons of pressure for 10 minutes. After cooling, a plastic partwith edges as shown in profile in FIG. 3 was removed from the mold.

The molded piece was irradiated at 4 MR. At 300° F. this material had a100% modulus of 51 psi, a tensile strength of over 190 psi, and anelongation of over 550%. The piece was expanded as described in ExampleIII. Pressure-sensitive transfer tapes and hot-melt adhesive wereapplied to the molded piece as described in Example I. The tapes wereallowed to build adhesion to the plastic piece overnight.

The plastic piece was wrapped around a 2-inch diameter cable, and theraised portion on one edge was pressed into the cavity near the otheredge. This was done easily by snapping one small part of the raised edgeinto a small part of the cavity and then pressing along. Once theplastic piece was in place, the release papers were removed and thepressure-sensitive silicone transfer tapes were pressed together. Theresulting sleeve was shrunk around the cable using a propane torch. Thesleeve formed a tight fit around the cable. The closure held securelyeven when heated vigorously with the torch.

EXAMPLES V, VI, VII AND VIII

Sleeves were prepared using the formulation and procedure described inExample IV, except instead of using Densil pressure-sensitive transfertapes, the following pressure-sensitive tapes were used:

a. Permacel P-257, thermosetting tape.

b. Permacel P-905, silicone tape.

c. Bostik 10-610-2, thermosetting transfer tape.

As in Example IV, the plastic pieces were wrapped around a 2-inchdiameter cable, and the raised portion on one edge was pressed into thecavity near the other edge. Once the plastic piece was in place, therelease papers were removed, and the pressure-sensitive tapes werepressed together. The resulting sleeve was shrunk around the cable usinga propane torch. In each case the sleeve formed a tight fit around thecable, and the closure held securely even when heated vigorously withthe torch.

The molded parts used in Example III and IV to produce wrap-aroundsleeves are designed to be fabricated by the more economical extrusionprocess. However, for production of small quantities for laboratoryexperimental use, it is more convenient to produce these parts by thecompression molding process.

I claim:
 1. A heat-shrinkable article comprising a heat-shrinkable sheethaving two edges adapted to form a closure, said edges beingheat-stable, at least one of said edges having thereon a pressuresensitive adhesive adapted, after compression against the other of saidedges to form a closure having a minimum lap-shear bond strength ofgreater than approximately 1.0 psi at 300° F., to maintain said closureat a temperature sufficiently high to shrink said heat-shrinkable sheet.2. A heat-shrinkable article in accordance with claim 1, wherein saidedges have mating portions so formed that, after formation of saidclosure and shrinking of said heat-shrinkable sheet, said closure is notsignificantly thicker than said sheet.
 3. A heat-shrinkable article inaccordance with claim 1, wherein said edges contain a built-in aligningand holding device.
 4. A heat-shrinkable article in accordance withclaim 1, wherein said pressure sensitive adhesive is a thermosettingadhesive.
 5. A heat-shrinkable article in accordance with claim 1,wherein said heat-shrinkable sheet has been irradiated to a dosagesubstantially greater than that required to impart heat-shrinkableproperties thereto.
 6. A heat-shrinkable article in accordance withclaim 4, wherein said pressure sensitive adhesive is a thermosettingacrylic pressure sensitive adhesive.
 7. A heat-shrinkable article inaccordance with claim 4, wherein said pressure sensitive adhesive is athermosetting rubber/resin pressure-sensitive adhesive.
 8. A process formaking a heat-shrinkable article comprising the following steps: forminga heat-shrinkable sheet having two edges adapted to form a closure, saidedges being heat-stable, and pressing against at least one of said edgesa pressure-sensitive adhesive adapted, after compression against theother of said edges to form a closure having a minimum lap-shear bondstrength of greater than approximately 1.0 psi at 300° F., to maintainsaid closure at a temperature sufficiently high to shrink saidheat-shrinkable sheet.
 9. A process for ensleeving an article comprisingthe following steps: wrapping about an article to be ensleeved aheat-shrinkable article comprising a heat-shrinkable sheet having twoedges adapted to form a closure, said edges being heat-stable, at leastone of said edges having thereon a pressure sensitive adhesive adapted,after compression against the other of said edges to form a closurehaving a minimum lap-shear bond strength of greater than approximately1.0 psi at 300° F., to maintain said closure at a temperaturesufficiently high to shrink said heat-shrinkable sheet, compressing saidtwo edges together so as to form a closure, and heating saidheat-shrinkable article to a temperature sufficiently high to shrinksaid heat-shrinkable sheet.